Neutron detection efficiency for the measurement of the

We report a measurement of the neutron detection efficiency for an array of neutron detectors behind a lead-steel wall consisting of 10.16 cm thick lead bricks sandwiched between 3.18 cm steel plates. The neutron detection efficiency was obtained from the ratio of coincidence to single-arm proton cross sections using the gamma+{sup 2}{sub 1}H -->p+n reaction. Knowledge of the neutron detection efficiency was necessary to extract the cross section for the exclusive {sup 2}H(e,e'n){sup 1}H reaction, which we used to obtain the elastic magnetic form factor G{sup n}{sub M} of the neutron. The measurements for three different neutron energies were carried out at the MIT-Bates Linear Accelerator Center with an incident electron beam energy of 254 MeV.